Joist/Wall Plate Position around Blocked Up Fireplace

[Gizzydash]

Hi All,

Picture attached of the setup I have for my fireplace (blocked up and not in use). Apologies for the dodgy powerpoint plan!

I'm replacing the joists/wall plates in this room and wondering if there are any requirements about how close the wall plates/joists can be to the concrete blocks under the hearth?

The closest guidance i've come across is '40mm from the outer surface of a masonry chimney' for combustable materials (except skirting etc). I'm not sure what constitutes the 'outer surface' of a masonry chimney when the flue/recess is behind a wall running straight across the room, or if the concrete blocks making up the underside of the hearth are considered part of the outer surface, so I have to leave a 40mm gap to these?

Thanks

 

[tony1851]

If the fireplace is blocked up (properly, with brick or block and not just a sheet of plasterboard or hardboard) then you don't need to consider any of the fire-safety regs.

 

[Gizzydash]

Yes, there are bricks blocking it up will become what I think is known as a faux fireplace and will retain a small hearth as I can't be bothered digging out the hearth that's there!

 

[^woody^]

Leave a faux 40mm then

 

[Gizzydash]

Thanks woody

If I am to future proof it as such and potentially want to open the fireplace up again at some point - or if future owners want to I understand the distances are:

• 200mm from inside surface of flue or fireplace recess - think i'm fine on that point as the recess is tiny, surprised they could even fit a fire in it tbh
• And as you say woody, 40mm from the outer surface of a masonry chimney or fireplace recess unless it is skirting board, dado etc etc.

So from my pic attached am I ok with new wall plate running around that sleeper wall and joists bearing onto it even up to 10mm from the wall or constructional hearth? The BC guidance is 40mm from the outer surface of a masonry chimney OR fireplace recess - assuming the fireplace recess would be the tiny opening in the middle i'm well away from that, easily over 100mm. Maybe i'm interpreting that guidance incorrectly though. Even if it's 40mm from the outer surface of the masonry chimney - what is the outer surface, is it the entire wall my fireplace is behind and right out to the end of the constructional hearth?

 

[Gizzydash]

Reason I raise the point around the 40mm above is that BC guidance doc also says that if the end of a joist is supported on masonry, the end bearing should not be less than 90mm. I assume a joist sitting on a sleeper wall fits this category and i therefore need to have a bearing of min 90mm. If I need to leave gaps of 40mm around the fireplace, that means I need a 130mm gap in total to get a sufficient bearing for the joist, but a sleeper wall is only ~100mm wide

 

[tony1851]

Where does it state a minimum bearing of 90mm?
In my old copy of timber joist load/span tables, it advises a minimum bearing of 38mm.

 

[Gizzydash]

Yes, 4th edition of Eurocode 5 states minimum bearing of 40mm, for some spans 50mm and longer for practical reasons. Attached is in the technical booklet from BC (done in 2012)...

 

[tony1851]

The 40mm distance applies to the proximity of structural timber to the flue, not the hearth.
There is no problem with timber joists being up against or alongside the hearth - see attached.

 

[Gizzydash]

ok, great, i'll work on that basis then. I'll leave a gap around the hearth so not to be butting timber up against masonry, but not 40mm. As for the joist bearing distance i'll work from the Eurocode 5 guidance of min 40mm, can only assume the local BC guidance is a bit dated at 2012. Thanks for all the info - really helpful as usual